CYA/pH and calcium hardness questions

[chem geek]

According to my calculations with your data, to go from 7.9 to 7.4 pH with your numbers you would need to add 5.2 pounds of Sodium Bisulfate solid (93.2% purity), not 3 pounds. If you were to use Muriatic Acid instead, you would need 8.2 cups. I'll bet the recommendations were based on an "assumption" of a TA of 80 (with a CYA of 150 or some other combination).

And yes, as Janet said, you were at a little risk of scaling and/or cloudiness at a pH of 7.9, but at a pH of 7.4 you'll be fine. The higher pH still reduces chlorine's effectiveness, but not as much as if you didn't have CYA. At 7.9 pH you have 0.018 ppm disinfecting chlorine (HOCl) while at 7.4 pH you have 0.021 ppm disinfecting chlorine.

As for your chlorine level with your high 150 CYA, you are a little on the low side and should have closer to around 10 ppm of chlorine to get decent algae prevention (disinfecting chlorine level of 0.029). If your pool is exposed to sunlight, you might lose quite a lot of chlorine each day (even with the CYA protecting it) and have difficulty keeping it this high. If this were earlier in the swimming season, I'd recommend further drain and refill dilution to lower your CYA, but since it's nearing the end of the season you can ride this out with high chlorine and then hope for a CYA reduction over the winter.

Richard

[mccato]

Thanks for your reply, Richard. That is very good information!